1. Field of the Invention
The present invention relates to an exposure apparatus including a support configured to support a projection optical system and a device manufacturing method using the exposure apparatus.
2. Description of the Related Art
Conventionally, in processes for manufacturing a semiconductor device including a micropattern, such as a large scale integrated circuit (LSI) or a very large scale integrated circuit (VLSI), a pattern formed on a reticle (mask) is projected onto a substrate with a reduced projection exposure apparatus. Since the substrate is coated with a photosensitive material, the pattern is transferred to the substrate. In order to meet a demand for finer micropatterns that are required in highly-integrated semiconductor devices, resist processes have improved and exposure apparatuses have become capable of handling highly-integrated semiconductor devices.
In an exposure apparatus configured to perform micropattern exposure, transmission of a vibration from the floor on which the exposure apparatus is placed to the exposure apparatus can cause deterioration in overlay precision and precision of exposure images. Waiting the vibration to cease, however, will result in lower throughput. Further, vibration tolerance is even more critical for a next-generation exposure apparatus using extreme ultraviolet (EUV) light.
Japanese Patent Application Laid-Open No. 3-121328 discusses a technique to reduce such a vibration by measuring vibration of a vibration control base having an acceleration sensor. FIG. 12 illustrates a configuration discussed in Japanese Patent Application Laid-Open No. 3-121328.
A vibration control base 1012 is supported by an air mount 1011. Air is supplied to the air mount 1011 via a control valve 1015. An acceleration sensor 1013 is mounted on the vibration control base 1012. A controller 1014 controls an opening of the control valve 1015 according to an acceleration signal detected by the acceleration sensor 1013. As a result, the vibration of the vibration control base 1012 is controlled.
Further, Japanese Patent Application Laid-Open No. 2005-294790 discusses a configuration in which a vibration transmitted from a first part to a second part is controlled. The first part is clamped to a base arranged on a floor and the second part is clamped to a frame configured to support a projection optical system. FIG. 13 illustrates the configuration discussed in Japanese Patent Application Laid-Open No. 2005-294790.
In FIG. 13, a gas spring 73, which is arranged between a first part 69 and a second part 71, is configured to control transmission of the vibration. Further, the position of the second part 71 relative to the first part 69 is controlled by a position control system.
The position control system includes a reference object 200 supported by the first part 69 via a reference support structure 201 (reference spring), a position sensor 202 mounted on the second part 71, and an actuator 203 arranged between the first part 69 and the second part 71.
The position sensor 202 detects a distance between the reference object 200 and the position sensor 202. The actuator 203 is controlled according to a detection signal from the position sensor 202.
However, in a case where a vibration of a supporting member that supports a projection optical system is measured by an acceleration sensor as discussed in Japanese Patent Application Laid-Open No. 3-121328, it is difficult to precisely detect a low-frequency vibration below 1 Hz according to a performance characteristic of the acceleration sensor.
On the other hand, in a case where a distance between the reference object 200 supported by the first part 69 and the position sensor 202 supported by the second part 71 is measured as discussed in Japanese Patent Application Laid-Open No. 2005-294790, measurement error may increase due to different ambient environment surrounding the reference object 200 and the position sensor 202. Here, the ambient environment includes such factors as temperature, humidity, and pressure.
Further, if the position of the second part 71, which is a supporting member that supports the projection optical system, is controlled according to a measurement of the vibration using the position sensor 202 and the reference object 200, the second part 71 may oscillate according to the natural vibration frequency of the reference spring, which supports the reference object 200.